Yes, the Captain could make him do anything...
His afternoon walks now were prolonged agonies.

He would turn his head at every moment, would stare into dark corners, would start at the sound of steps.

His sleep now was broken with horrid dreams, and he would jump up and cry out; and one night he actually dreamt of his dead-white road and the sounds that came up from below the hill, the bell and the sea, and the distant rattle of the little carts.
Then the Captain drew near to the very house itself.

He haunted Orange Street, could be seen lounging against a lamp-post opposite the High School, looked once into the very garden of the Coles, Jeremy watching him with beating heart from the schoolroom window.

It was incredible to Jeremy that no one else of the house perceived him; but no one ever mentioned him, and this made it appear all the more a dream, as though the Captain were invisible to everyone save himself.